The invention relates to a melting furnace, especially an arc furnace, in which the furnace wall contains at least one water cooling box of welded sheet steel disposed above the melt level, whose surface facing the interior of the furnace is provided with projections which facilitate the adherence of a refractory protective coating formed on this surface.
To extend the life of the lining of melting furnaces, especially arc furnaces, water cooling boxes of welded steel plates have been installed in the furnace wall in back of the brickwork lining for the purpose of cooling the latter. This has not proven to be completely satisfactory, inasmuch as the severe heating of the interior surface of the refractory bricks covering the water cooling box and the cooling action exercised on their exterior surface creates the danger that the bricks may become distorted and break away, exposing the surface of the water cooling box directly to the arc heat of the furnace. Not only does this result in the occurrence of cracks in the walls of the water cooling boxes, especially when the wall thickness is greater than 12 mm, and in the burning of holes into the wall of the water cooling boxes resulting in cooling water leakage and the danger of explosion, but also the thermal efficiency of the furnace is reduced thereby.
A new approach has been taken to the prevention of these disadvantages. The refractory bricks have been removed in the area of the water cooling boxes or cooling tubes as the case may be, and instead the cooling element surface facing the furnace interior has been constructed such that the ability of metal or slag splashes to adhere to it is greatly increased, so that during operation a protective layer of refractory slag builds up on it and adheres tightly to it, protecting the cooling elements and assuring a good heating efficiency. In the system disclosed by German Offenlegungsschrift 2,354,570, the cooling means are constructed of a main body of cast iron or copper and a number of cooling tubes cast directly in the main body, while the surface facing the interior of the furnace is corrugated or is formed with bricks discretely embedded in and projecting from the said surface in order to increase the adhesive-holding ability thereof. In the solution proposed by German Offenlegungsschrift 2,502,712, the cooling elements are water cooling boxes made by welding sheet steel, whose surfaces exposed to the interior of the arc furnace are provided with a plurality of ribs or rod-like projections in a lattice or checkerboard arrangement. After the furnace is placed in operation, a refractory coating of slag forms on the initially bare surface of the cooling boxes in a thickness of up to 20 mm; this coating adheres firmly and assures a good thermal efficiency of the arc furnace.
What is disadvantageous in the cooling system disclosed by German Offenlegungsschrift 2,354,570 is the relatively high cost of the manufacture of the cooling elements constructed as castings. Disadvantageous in the approach disclosed by German Offenlegungsschrift 2,502,712 is the danger that, when the furnace is started up, some of the projections may melt away before a protective layer of slag has formed on them, and then a sufficiently thick protective coating will no longer be able to form at such points, and that, prior to the formation of a suitable coating, the danger of strike-overs by the arc to the water cooling boxes exists, resulting in greater danger of explosion due to water leakage.